Activities of enzymes required for the conversion of 4-carbon TCA cycle compounds to 3-carbon glycolytic compounds in human diploid fibroblasts.

Phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase activities were localized in the mitochondrial (particulate) fraction of human diploid fibroblasts (HDF). Malic enzyme, malate dehydrogenase (MDH) and glutamate oxalacetate transaminase (GOT) were distributed between the mitochondrial and cytosolic (soluble) fractions, the latter two enzymes being more equally distributed than malic enzyme, which was largely cytosolic. The specific activities of mitochondrial PEPCK and cytosolic malic enzyme, MDH and GOT increased during cell growth. The results support an active conversion of 4-carbon tricarboxylic acid cycle intermediates to 3-carbon glycolytic intermediates in HDF.